Thunder Lake Trail + Lion Lake Trail out and back

Rocky Mountain National Park · 8.01 mi out and back · about 3 hr 35 min

View mapPlan a trip

Distance8.01 micomputed

Elevation gain1,851 ftcomputed

Elevation loss1,850 ftcomputed

Est. time3 hr 35 minNaismith's rulecomputed

DifficultyNot ratedno source has rated itunknown

Highest: 11,115 ft
Lowest: 10,018 ft
Route type: One way or out and back
Surface: Not mapped
Offline

Schematic preview drawn from the trail geometry. No basemap yet; do not use for navigation. Start = circle.

Overview

Thunder Lake Trail + Lion Lake Trail out and back is mapped as a trail of 8.01 mi in Rocky Mountain National Park. It is not a loop: you walk it one way or out and back.

It runs between 10,018 ft and 11,115 ft above sea level, a difference of 1,096 ft.

Mapped along or near the trail: 1 viewpoint.

Estimates

Computed effort band: hard (from length and climb; not an official difficulty).
Estimated time 3 hr 35 min one way by Naismith's rule, which assumes steady walking and adds time for climbing. Real time varies.

Before you rely on this

No water source is mapped for this trail. That may only mean nobody has mapped one, so carry your own water.
Check the land manager for closures, seasonal rules and permits before you go; none of that is verified here.

Hard effortCamp sites nearby Long (8 mi or more)Viewpoints

Elevation

Hover, tap, or use the arrow keys on the chart to read a point; it is shown on the map too.

Elevation along the trail from start (left) to end (right) as drawn. Values are computed from USGS 3DEP 1/3 arc-second DEM (public domain), sampled about every 10 m and smoothed. Shaded bands are sections steeper than about 12% (7 climbing in red, 7 descending in blue).

Steep sections (14)

394 ft to 0.15 mi: about 15.8% uphill (from the elevation model, so rough)
1.57 mi to 1.70 mi: about 12.5% downhill (from the elevation model, so rough)
1.77 mi to 1.83 mi: about 13.4% downhill (from the elevation model, so rough)
1.90 mi to 2.03 mi: about 19.3% uphill (from the elevation model, so rough)
2.25 mi to 2.32 mi: about 18.8% uphill (from the elevation model, so rough)
2.49 mi to 2.71 mi: about 18.5% uphill (from the elevation model, so rough)
3.16 mi to 3.63 mi: about 16.1% uphill (from the elevation model, so rough)
4.38 mi to 4.86 mi: about 15.9% downhill (from the elevation model, so rough)
5.30 mi to 5.52 mi: about 18.6% downhill (from the elevation model, so rough)
5.64 mi to 5.77 mi: about 14.9% downhill (from the elevation model, so rough)
5.99 mi to 6.12 mi: about 18.5% downhill (from the elevation model, so rough)
6.19 mi to 6.25 mi: about 13.2% uphill (from the elevation model, so rough)
6.32 mi to 6.45 mi: about 12.5% uphill (from the elevation model, so rough)
7.87 mi to 7.94 mi: about 15.6% downhill (from the elevation model, so rough)

Before you go

Parking: No parking is mapped near the start. not verified
Trailhead and directions: Start at 40.22208, -105.64512. Directions to the start ↗
Permits and fees: We have no verified permit or fee details. Official pages: Rocky Mountain National Park ↗, Rocky Mountain Wilderness ↗, Boulder County ↗ (we have not recorded when these were last checked). Rocky Mountain National Park: fees and passes ↗ (checked 2026-10-17) Rocky Mountain National Park: timed entry permits ↗ (checked 2026-10-17) not verified
Dogs: No dog rule is tagged. not verified
Water: No water is mapped. Carry your own. not verified
Toilets and facilities: 1 toilet mapped. mapped by OpenStreetMap contributors
Accessibility, bikes and horses: No access details are tagged. not verified
Seasonal rules, closures and hazards: Not verified here. Check the land manager (Rocky Mountain National Park ↗), Rocky Mountain National Park: current conditions ↗ (checked 2026-10-17) and read the hiker condition reports below. No report does not mean the trail is open or safe. not verified

Weather at the trailhead

Sun49° / 32°Mostly Sunny0% precip

Mon46° / 32°Mostly Sunny13% precip

Tue47° / 34°Mostly Sunny11% precip

Wed49° / 36°Mostly Sunny2% precip

Thu51° / 36°Mostly Cloudy then Chance Rain Showers46% precip

Fri48° / 30°Rain And Snow Showers Likely66% precip

Sat40° / –Chance Snow Showers45% precip

Today: sunrise 7:15 AM, sunset 6:18 PM (computed from the trailhead location).

Forecast for the trailhead area from the U.S. National Weather Service, updated Oct 18, 12:46 AM. Mountain weather changes fast and can differ a lot by elevation: check the official forecast for your route before you go.

Recent conditions

Reports come from Arête members, not from land managers. They show when something was seen, not whether it is still true. Check official sources before you go.

No condition reports in the last 30 days. Conditions are unknown, not necessarily good.

Reviews

No reviews yet, so there is no rating to show. We never invent ratings. Sign in to be the first to review this trail.

Photos and places from hikers

Added by community members and checked by our team before they appear. Photos have their location data removed. These are not official information.

No approved photos or places yet.

Along the way

Sights

Viewpoint4.82 mi from start
Unnamed OSM ↗

Trailhead and facilities

Camp site420 ft from startFee mapped
Thunder Lake Stock Campsite OSM ↗
Camp site0.20 mi from startFee mapped
Thunder Lake CS #1 OSM ↗
Toilets
Unnamed OSM ↗

Parking and toilets shown are within about 0.25 mi of the trail start.

Points come from OpenStreetMap contributors and can be missing, moved or out of date. How we label data.

Nearby trails

Arête-built route from mapped trails

Assembled by Arête from mapped trail segments. Not an official or recommended route.

Thunder Lake Trail · 134 ft (part of the mapped trail)
Thunder Lake Trail · 0.16 mi (part of the mapped trail)
Thunder Lake Trail · 1.72 mi (part of the mapped trail)
Lion Lake Trail · 2.09 mi
Lion Lake Trail · 2.09 mi · walked back
Thunder Lake Trail · 1.72 mi (part of the mapped trail) · walked back
Thunder Lake Trail · 0.16 mi (part of the mapped trail) · walked back
Thunder Lake Trail · 134 ft (part of the mapped trail) · walked back

Starts at a derived trailhead (2 mapped trails start within 150 m), no mapped parking within 400 m; the route starts at the nearest mapped trail junction, 29 m from that point. Built by Arête from the graph of mapped trail segments (OpenStreetMap). Segments join where their ends are within 12 m of each other or one ends on another's line (a T-junction). A loop returns to its start without repeating a trail section; an out-and-back goes to a mapped trail end and returns the same way, so its length counts both directions. Names come only from the mapped trails it uses. Length is measured on the joined line; elevation is computed from USGS 3DEP. Not an official or recommended route.

Data, sources and how the numbers are made

Length	8.01 micomputed
Route type	Out and backcomputed
Surface	Unknownunknown
Difficulty	Unknownunknown
Elevation gain (as drawn)	1,851 ftcomputed
Elevation loss (as drawn)	1,850 ftcomputed
Estimated duration	about 3 hr 35 min one way as drawn (Naismith's rule)computed
Official verification	Not verified by an official sourceunknown

Length is measured from the route geometry in the source data, so it can differ from signed or official distances. Gain and loss describe the direction the line is drawn; the route view above shows the other direction and out and back. Elevation is computed from USGS 3DEP 1/3 arc-second DEM (public domain), sampled about every 10 m and smoothed.

Frequently asked questions

How long is Thunder Lake Trail + Lion Lake Trail out and back?

Thunder Lake Trail + Lion Lake Trail out and back in Rocky Mountain National Park is 8.01 mi long, measured from its route geometry in OpenStreetMap data. Signed or official distances can differ.

How much elevation does Thunder Lake Trail + Lion Lake Trail out and back gain?

Walking from the start to the end as drawn, it climbs about 1,851 ft and descends about 1,850 ft, between 10,018 ft and 11,115 ft. These are computed from the USGS 3DEP elevation model and can differ from other apps; the other direction swaps climbing and descending.

How hard is Thunder Lake Trail + Lion Lake Trail out and back?

Difficulty is unknown: no source we use rates this trail, and we don't guess. Use the length and elevation gain to judge it for yourself.

How long does Thunder Lake Trail + Lion Lake Trail out and back take?

About 3 hr 35 min one way for a fit hiker, by Naismith's rule from the length and climb. It is an estimate: allow more for rest, photos, heat, altitude and weather.

Where does Thunder Lake Trail + Lion Lake Trail out and back start?

The route starts near 40.2221, -105.6451 (Rocky Mountain National Park, Rocky Mountain Wilderness, Boulder County). Use the Directions button to open it in your maps app.

Are dogs allowed on Thunder Lake Trail + Lion Lake Trail out and back?

Not tagged in OpenStreetMap, so it is unknown. Check posted signs and the land manager's website.

Is there water, parking or a toilet at Thunder Lake Trail + Lion Lake Trail out and back?

Mapped in OpenStreetMap near this trail: 0 water points, 0 parking areas, 1 toilet. Mapped water is not tested or guaranteed: carry your own. Fees and permits are not included here; check the official page.

Trail data can be wrong or out of date, and Arête is not an emergency service. Check official sources, weather and closures before you go.

Directions